The present invention relates to clutches, and more particularly, relates to an active indexing bi-directional overrunning clutch.
In a typical all wheel drive system, a front axle is a primary drive, while torque to the rear axle is transferred if and when the average speed of the front wheels is faster than the average speed of the rear wheels. The torque transfer generally occurs if the front wheels have excessive slip and it also may occur during low speed cornering situations. A clutch works as a mechanical disconnect which prevents torque from being transferred from the rear axle to the front axle. Currently known in the prior art are single direction clutches and bi-directional overrunning clutches and also clutches that use hydraulic systems to effect changes thereon. The bi-directional overrunning clutch differs from the single directional, because it works in both the clockwise and counter clockwise rotational directions. With the bi-directional clutch, if the output of the rear axle is rotating faster in one direction than the input from the front axle there is no torque transmission but if the input speed is equal to the output speed the unit will lock. Also, while in four wheel drive and in the reverse gear, the overrunning clutch locking function direction must be changed from the forward direction to the reverse direction. The bi-directional clutch will switch the operation mode dependent on the prop shaft or input speed direction. The use of the bi-directional overrunning clutch provides benefits with regards to braking, stability, handling, and drive line durability.
In a typical ABS braking event, disconnecting the front and rear drive line during braking helps to maintain braking stability. During the ABS braking event the locking of the rear wheels must be avoided for stability reasons and hence, the brake systems are designed to lock the front wheels first. During an ABS event, torque transfer from the rear axle to the front axle may disturb the braking system because of potential instabilities on the slippery surfaces. The use of a bi-directional overrunning clutch will decouple the rear drive line once the rear wheels spin faster than the front wheels and will provide excellent braking stability.
A bi-directional clutch also reduces likelihood of throttle off over steering during cornering of the vehicle. During a throttle off maneuver the clutch will decouple the rear drive line thus transferring all the engine braking torque to the front wheels which reduces the chance of a lateral slip on the rear axle. Therefore, the vehicle tends to under steer on a throttle off condition, a situation which is generally considered easier to manage by the average vehicle operator.
Bi-directional clutches have provided several advantages to the all wheel drive systems. Problems may occur during low speed when a vehicle is in a reverse rolling position and the vehicle operator then selects a drive position. After acceleration backlash may occur in the drive line which allows inertia in the engine and other components to build thus transmitting a torque to the rear drive line which induces an engagement phenomenon within the bi-directional clutch mechanism as the vehicle drive line goes from a reverse gear to a forward gear. This phenomenon is often reported by vehicle owners and is undesirable. Therefore, there is a need in the art for a bi-directional clutch mechanism that has active indexing which will reduce the engagement phenomenon associated with a switch from a forward to reverse gear or reverse to forward gear in an all wheel drive vehicle system.
One object of the present invention is to provide an active bi-directional overrunning clutch capable of being indexed.
Another object of the present invention is to provide an active low speed worm gear bi-directional overrunning clutch.
Yet a further object of the present invention is to provide a clutch with active indexing that will reduce the clunk phenomenon of prior art bi-directional clutch mechanisms.
Another object of the present invention is to provide a clutch that will index during rotation reversal before torque is transmitted through a prop shaft of a vehicle.
Yet a further object of the present invention is to reduce the speed difference between the prop shaft and the rear axle pinion shaft which will lock the clutch before any torque transmission.
To achieve the foregoing objects the active bi-directional overrunning clutch includes an oil housing. The clutch also includes a flange rotatably supported with respect to the oil housing. An input shaft is connected to the flange. A plurality of rollers are in contact with the input shaft and a coupling. The clutch also includes a roller cage wherein that roller cage positions the plurality of rollers with respect to the input shaft and the coupling. The clutch further includes a friction ground member in contact with the roller cage and a worm gear in contact with the friction member.
One advantage of the present invention is that active indexing of a bi-directional clutch will occur prior to torque transfer via an electric motor.
A further advantage of the present invention is the reduction of the clunk phenomenon by active indexing of the bi-directional clutch mechanism.
A further advantage of the present invention is the reduction in speed difference between the prop shaft and the rear axle pinion shaft because of the indexing of the clutch, which therefore, locks the clutch before any torque transmission.
A further advantage of the present invention is a low speed indexing of the clutch from either the reverse to the forward gear or vice versa.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and appended claims, taken in conjunction with the accompanying drawings.